Carb-related symptoms in IBS due to colon hypersensitivity to distention

Reuters Health Information: Carb-related symptoms in IBS due to colon hypersensitivity to distention

Carb-related symptoms in IBS due to colon hypersensitivity to distention

Last Updated: 2016-10-28

By Will Boggs MD

NEW YORK (Reuters Health) - Carbohydrate-related symptoms in
irritable bowel syndrome (IBS) result from colon
hypersensitivity to distention, not from excessive gas
production, researchers from the U.K. report.

"This paper provides evidence of how fermentable
carbohydrates can distend the colon," Dr. Giles Major from the
University of Nottingham told Reuters Health by email.

"It provides a mechanistic basis for the clinical
observation that reducing such carbohydrates in the diet can
reduce feelings of bloating and discomfort, but it also makes an
important point: that, in this group at least, IBS patients did
not have more gas in their colons - they got more discomfort
from the same amount of gas as was found in others," he said.

Consumption of fermentable carbohydrates - termed
fermentable oligosaccharides, disaccharides, monosaccharides,
and polyols (FODMAPs) - has been associated with an exacerbation
of symptoms in patients with IBS. Dietary changes reducing the
consumption of those carbohydrates result in a reduction of
symptoms, but the mechanism remains unclear, according to Dr.
Major and colleagues.

The team conducted a three-period crossover study of 29
adult patients, examining changes in the Composite Symptom Score
(CSS). The CSS includes four symptoms: gas/flatulence, bloating,
pain/discomfort, and diarrhea, with each symptom scored on a
scale from 0 (none) to 3 (severe/disabling).

One in five IBS patients (21%) experienced a significant
increase in symptoms (change in CSS >=3) after the glucose
control and 45% reached this threshold after inulin, a poorly
absorbed carbohydrate. Fructose consumption increased symptoms
significantly in 38% of IBS patients.

Volunteer response rates were lower for inulin (3/29) and
fructose (3/29) but not significantly different for glucose
(2/29), the researchers report in Gastroenterology, online
October 13.

Although colonic volume and breath hydrogen in IBS patients
were higher for both fructose and inulin than for glucose, the
patterns of change were similar among volunteers.

Peak rise in colonic gas correlated with symptoms in
patients after inulin, but there was no difference in this
variable between patients who did and did not report symptoms.

For fructose, the only variable that differed significantly
between those who reported symptoms and those who didn't was
their initial somatization score (median, 8 in those with
symptoms vs. 5 in those without, where less than 7 is normal).

"The study therefore offered no evidence that patients who
reported symptoms produced more colonic gas than those who did
not," the researchers conclude. "An alternative hypothesis would
be that, as has been shown with lactose malabsorption, the
patients with symptoms had a lower sensory threshold for
reporting."

"Patients who report symptoms relating to fermentable
carbohydrate may be accurately assigning the cause of their
problems," Dr. Major said. "The same patients may also have
visceral hypersensitivity. Treating with the two modalities of
dietary modification and pharmacotherapy could help."

"An unknown quantity in our study is the role of the
microbiota," Dr. Major added. "It may be that certain
microbiomes induce more gas production. There may also be small
molecule products of fermentation that mediate nerve signaling.
The prospect of linking microbiome signatures to dietary
sensitivity holds real promise tor personalized care of
patients."